The present invention concerns a method of and device for optimizing the cutting indication in a machine that cuts material, especially stacked sheets of paper, cardboard, etc.
German 3 116 292 A1 discloses a method of optimizing the cutting indication in a material-cutting machine. A hydraulically actuated beam descends on the sheets of material stacked on a bench to hold the material fast before it is cut and the beam's holdfast force is reduced before the beam descends onto the material.
During cutting indication the holdfast beam descends onto the material to be cut to monitor the course of the cut and correct any error in the orientation of the stack. The known material-cutting machine has a special switch that reduces the compression of the hydraulic fluid and hence the beam's holdfast force in order to prevent injury in the event an operator's finger intervenes between the holdfast beam and the stack during cutting indication and simultaneous correction of the stack's orientation. Safety regulations provide that the beam's holdfast force be no more powerful during cutting indication than 500N. The beam's holdfast force can accordingly be reduced even further in the known material-cutting machine in order to completely rule out any risk to the operator. The machine includes for this purpose two pressure-regulating valves, one that limits the compression of the hydraulic fluid to maintain the beam's holdfast force at no more than 500N and the other inside a compressor. Associated with the mechanism that actuates the cutting indication is an electric circuit that in order to protect the operator while the material is being cut, activates a light barrier in the machine. When the light across the light barrier is interrupted, the circuit generates a signal that deactivates the first valve and activates the second, preferably limiting the force on the holdfast beam to 100N. The holdfast beam descends at high speed as long as the light barrier is not interrupted, although the static and dynamic cutting-indicator forces are low and the descent of the holdfast beam is slow when operations are conducted below the holdfast beam.
One drawback to the aforesaid material-cutting machine is that the holdfast beam descends slowly and with diminished force while the operator is working in the vicinity of the light barrier that is conventionally present in material-cutting machines. It should basically be attempted on the other hand to ensure that the holdfast beam comes to rest gently against the stack, especially when the sheets are thin. Aside from that, it is also considered a drawback from the aspect of minimizing the unproductive motions of the holdfast beam for the rate of the holdfast beam's descent to be initiated by the light barrier, which is so far from the holdfast beam and the blade, leading to premature deceleration of the descent when the light barrier engages.